STAFF REPORT IBD: Climate change may have determined the fate of the ancient worlds most expansive civilization. A new study suggests that the waning of monsoons spurred both the rise and fall of the Harappans, who flourished in the floodplains of the Indus Valley thousands of years ago.Small floods driven by the rains nourished the crops of early cities but proved unreliable generations later, researchers have recently reported online in the Proceedings of the National Academy of Sciences.“The Indus people were a Goldilocks civilization,” says Liviu Giosan, a geologist at the Woods Hole Oceanographic Institution in Massachusetts. “They settled when the floods were just right, and then they disappeared when that window of opportunity disappeared.”Sediments unearthed and dated by the researchers showed a remodeling of the landscape over time. About 10,000 years ago, flooding rivers in parts of India, Pakistan and Afghanistan changed behaviour as monsoon rains weakened. Instead of dumping loads of sediment that built up the land, the rivers began to cut out valleys.“They were smart in picking sites with just enough water,” says Peter Clift, a sedimentologist at Louisiana State University in Baton Rouge and coauthor of the new study.To really understand how climate change played out in each city, says Wright, archaeologists will need to move beyond the big picture and dig up new clues.